Also I read osmething on here earlier that said that the 6.7 Did have a silencer ring but you had to take it off by unscrewing 3 bolts or something like that then it would come out then you replaced the screws also you should also have a muffler similar to what I had It is a big round plastic contaner before your turbo on your intake side. Should be able to cut the top off and pull the insides out. Then your whistle will be louder.
There are three metal pins/dowels that are at noon, four and eight o'clock on the turbo housing. drill them out and the silencer doughnut comes out with a good tug.